CCNA Network Infrastructure and Connectivity Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  At the Transport layer, the TCP/IP model uses segments, while the OSI model uses packets.

  Why it's wrong here

  This is incorrect because the Transport layer in both the OSI and TCP/IP models uses the same PDU names: TCP segments or UDP datagrams. The term 'packet' is specifically reserved for the Network layer (Layer 3), where an IP header is added. Therefore, saying the OSI Transport layer uses packets misidentifies the PDU.

• ✓

  In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function.

  Why this is correct

  This is correct. The OSI Network layer (Layer 3) and the TCP/IP Internet layer are conceptually equivalent; both encapsulate the Transport layer PDU (segment or datagram) into an IP packet by adding a Layer 3 header. This packet is then passed down to the Data Link layer for framing. Thus, the function is identical in both models.

• ✓

  The term 'frame' is used at the Data Link layer in both the OSI and TCP/IP models, and it contains the Layer 2 header and trailer.

  Why this is correct

  This is correct. In both the OSI and TCP/IP models, the Data Link layer produces a frame as its PDU, which encapsulates the network-layer packet by adding a Layer 2 header and a trailer (typically containing a frame check sequence). The term 'frame' is universally used at this layer regardless of the reference model. This framing is a common function across both architectures.

• ✗

  Encapsulation adds headers and trailers at each layer, so the PDU size decreases as data moves down the stack.

  Why it's wrong here

  This is incorrect because encapsulation adds protocol headers (and a Layer 2 trailer), which increases the overall PDU size at each lower layer. For example, a transport segment becomes a larger network packet once an IP header is added, and grows further as a data-link frame with its own header and trailer. The PDU size does not shrink; it expands as data moves down the stack.

• ✗

  The OSI model's Session layer is responsible for end-to-end flow control using TCP segments, while the TCP/IP model combines this into the Application layer.

  Why it's wrong here

  This is incorrect because end-to-end flow control is a Transport layer function (Layer 4), not a Session layer (Layer 5) responsibility. While the TCP/IP model indeed has no dedicated Session layer, the Transport layer (e.g., TCP) handles flow control via windowing in both models. The Session layer manages dialog control and synchronization, not flow control.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”